Setting null when sending data as form data in one-to-one relationships

[mahdiashtian]

my code:

 class UserSerializer(NestedUpdateMixin, serializers.ModelSerializer):
  skill = SkillSerializer(many=True, required=False)
  experience = ExperienceSerializer(many=True, required=False)
  education = EducationSerializer(many=True, required=False)
  profile = ProfileSerializer(required=True, instance=Profile)

 class ProfileSerializer(WritableNestedModelSerializer):
  child = ChildSerializer(many=True, required=False)
  foreigner = UserForeignerSerializer(required=False, allow_null=True, instance=UserForeigner)

When I send the data as a form-data, one-to-one relationships are lost and set to null
But when I make a request in the form of json, it is applied correctly, the request must be sent in the form of a form-data
Does anyone know what the problem is?